After LTE (Long Term Evolution) systems experienced version R8/9/10, a R11 technology is further put forward. At present, partial R8 products start to be gradually commercially used, and R9 and R10 need further product planning.
After experiencing stages of R8 and R9, R10 is added with many new features on the basis of R8 and R9, for example, pilot features such as DMRS (Demodulation Reference Signal), CSI-RS (Channel State Information Reference Signal) and the like, transmission and feedback features such as 8-antenna support, etc. Especially, an eICIC (enhanced Inter-Cell Interference Cancelling) technology considers an inter-cell interference avoiding technology on the basis of considering R8/9 ICIC. Technologies for solving inter-cell interference problems mainly consider cell interference avoidance under homogeneous networks at the beginning of the stage of R10, wherein the eICIC technology and a CoMP (Coordinated Multi-point) technology are mainly considered. Just as the name implies, the CoMP refers to that multiple nodes coordinate to transmit data to one or a plurality of UE under the same time frequency resource or different time frequency resources. This technology can reduce the inter-cell interference, improve the throughput rate of cell edges and expand the cell coverage. However, in consideration of more scenarios to be introduced into heterogeneous networks at the later discussion stage, the complexity of the CoMP technology and the time limit of discussion about R10, finally it is decided not to introduce additional CoMP standardization contents at the state of R10. However, CSI-RS can be designed in consideration of partial demands of CoMP and thus the CoMP technology is not discussed more deeply after the 60bis meeting.
At the SI (Study Item) of the early discussion stage of R11, uniform evaluation architecture is determined mainly by planning scenarios and various CoMP transmission technologies, and two stages of CoMP evaluation are carried out to demonstrate that the CoMP technology can obtain obvious performance gains. According to the CoMP SI conclusion which is recently completed, further studies need to be carried out to JT (Joint Transmission), DPS (Dynamic Point Selection), CS (Coordinated Scheduling) and CB (Coordinated Beamforming) in the CoMP technology.
Before studies are carried out to various CoMP technologies, it needs to firstly consider the differences of the CoMP technology with respect to R8/9/10, including how the CoMP control signaling supports the notification of CoMP measurement sets, how to support the demands of different CoMP transmission technologies, and how UE measure and report CSI (Channel State Information) of a plurality of nodes, wherein how UE measure and report CSI of a plurality of nodes is one of primary problems needed to be solved by the CoMP technology. According to current discussion, feedback of CoMP can be mainly divided into periodic feedback and aperiodic feedback, and aggregate channel information feedback and non-aggregate channel information feedback. The so-called aggregate channel information feedback refers to that channel information of a plurality of nodes is aggregated into channel information of one node for global feedback. For example, if a measurement set includes two nodes, channel information of node 1 is H1 and channel information of node 2 is H2, and at this moment, the UE firstly aggregate the channel information of the two nodes into a piece of big channel information H=[H1; H2] and then measurement related calculation and feedback are performed. Non-aggregate channel information feedback can be further divided into independent single-cell feedback and independent single-cell feedback plus inter-cell correction information. The so-called independent single-cell feedback refers to that measurement related calculation and feedback are independently performed according to the channel information of each node. The so-called independent single-cell feedback plus inter-cell correction information refers to that measurement related calculation is independently performed according to the channel information of each node, phase and/or amplitude information between nodes are calculated and fed back. For aggregate channel information, feedback of an aggregate CQI (Channel Quality Indicator) is included therein, and the aggregate CQI refers to that a CQI fed back by the UE side is an aggregate CQI measured corresponding to one or a plurality of pieces of CSI-RS configuration information, the UE find time frequency locations of corresponding CSI-RS by using a plurality of pieces of CSI-RS configuration information, thus measurement is performed to obtain precoding weight information and calculation is performed by using interference information obtained through other pilot frequency, and at this moment, suppose that data are transmitted to the UE by nodes corresponding to one or a plurality of pieces of CSI-RS configuration information, so as to obtain a CQI value corresponding to joint transmission performed by the plurality of nodes. Since one aggregate CQI may correspond to one or a plurality of pieces of CSI-RS configuration information for aggregation of measurement, for example, a measurement set possibly includes three pieces of CRS-RS configuration information, and at this moment, there are three possibilities to aggregate one piece of CSI-RS configuration information, three possibilities to aggregate two pieces of CSI-RS configuration information, one possibility to aggregate three pieces of CSI-RS configuration information, and totally there are seven possibilities. Therefore, there are multiple possibilities to aggregate the CQI and no possibility can be called an aggregate possibility.
For traditional R8/R9/R10 subscribers, since only the CSI of a serving cell needs to be fed back, the capacity of a single cell only needs to be considered for periodic feedback and aperiodic feedback on the same carriers, and especially for a PUCCH (Physical Uplink Control Channel), optimization of the feedback of a single cell is only needed. At present, in consideration of coding, HARQ (Hybrid Adaptive Request Retransmission) bit number, etc., for one UE, the maximum bit number of CSI feedback supported in a PUCCH uplink sub-frame is eleven. For the composition of the 11 bits, at most 4 bits of PMI (Precoding Matrix Indicator) and 7 bits of CQI (Channel Quality Indicator) in two code words can be considered (differential feedback of CQI between different code words is considered). Since CSI feedback of a plurality of cells needs to be considered in the CoMP technology, a PUCCH capacity of N*11 bits is required. However, the current PUCCH capacity cannot meet this requirement and thus a set of reasonable feedback solutions is needed to solve the problem that the PUCCH capacity is not enough. What can be easily conceived is to compress feedback signaling, but the CoMP technology has a higher requirement on the precision of CSI, especially JT and even JT-MU attach a higher requirement on the precision of CSI, thus the performance loss caused by compression may cause decrease of CoMP performance gains. Another possible consideration is to improve the capacity of the PUCCH, the feedback type of the PUCCH needs to be redesigned and thus it is bound to bring greater standardization efforts. If it is considered that the CSI feedback requirements are different between different modes of CoMP and adaptive switching of different modes possibly needs to be guaranteed, this feedback design may be more complex. Therefore, it is considered in discussion to introduce inter-node information that can guarantee flexible switching of coordinated transmission modes and/or a concept of aggregate CQI. In a recent meeting, it was discussed that the aggregate CQI can obtain performance similar to that obtained by introducing inter-node information and aggregate CQI, and the feedback of additional inter-node information is not introduced at this moment, and at present, whether to introduce the feedback of inter-node information is still under discussion in meetings. However, the introduction of the concept of aggregate CQI is considered in both the above two solutions. For the concept of aggregate CQI, it is to feed back a CQI value generated by aggregation of a plurality of nodes, and the number of aggregated nodes therein can be a combination of any number of nodes of all nodes in a measurement set. For example, if a measurement set includes six nodes, and at this moment, the possible combinations include sixty-three situations; and if the limitation of the maximum aggregated node numbers is considered, and at this moment, the combinations include forty-one possibilities. If UE feeds back once or a plurality of sub-frames feed back a plurality of aggregate CQIs of various situations, a base station side needs to know a combination of which nodes is fed back by the UE, and this point needs to be uniformly regulated on both the base station side and the UE side. Otherwise, the base station side cannot know which nodes the received fed-back aggregate CQI is the combination of.
Feedback for R10 can be mainly divided into periodic feedback and aperiodic feedback.
For aperiodic feedback, uplink authorization or random access authorization control signaling is needed to trigger the aperiodic feedback. Aperiodic feedback modes, as shown in Table 1, can be divided into the following types:
TABLE 1Aperiodic feedback modesPMI feedback typeNo PMISingle PMIMultiple PMIPUSCHWidebandMode 1-2CQIWideband CQIfeedbackUE SelectedMode 2-0Mode 2-2type(Sub-band CQI)Higher Layer-Mode 3-0Mode 3-1configured(Sub-band CQI)
Aperiodic report modes are configured to the terminal side via high-layer signaling eqi-ReportModeAperiodic.
Only when the base station side configures the terminal side to adopt transmission modes 3, 4, 8 and 9 and have a preceding matrix indicator (PMI)/(rank indicator) RI feedback configuration does an RI need to be fed back. For a wideband feedback mode 1-2, the terminal side needs to feed back a plurality of sub-band PMIs and a wideband CQI calculated based on the plurality of PMIs; for higher layer-configured sub-band CQIs, a mode 3-0 and a mode 3-1 are included; for the mode 3-0, the terminal side needs to feed back a wideband CQI and a plurality of sub-band CQIs, and both the wideband CQI and the sub-band CQIs are calculated based on code words: for the transmission mode 3, the calculation of CQI needs to consider different RI values; and for the transmission modes other than the mode 3, the CQI is calculated by supposing RI=1. For the mode 3-1, the terminal side needs to feed back a wideband PMI and then respectively calculate and feed back a wideband CQI and a plurality of sub-band CQIs according to the fed-back wideband PMI, wherein for transmission modes 4, 8 and 9, the calculated value of the CQI needs to be determined based on the values of RI; and for other transmission modes, the calculated value of the CQI is determined according to RI=1. For the sub-band CQIs of the mode 3-0 and mode 3-1, differential feedback is adopted. For UE selected sub-band feedback, a mode 2-0 and a mode 2-2 are included. For the mode 2-0, the terminal side needs to feed back a CQI shared by M Perfer sub-bands and a wideband CQI; for the transmission mode 3, the calculation of the CQI needs to consider different RI values; and for the transmission modes other than the mode 3, the CQI is calculated by supposing RI=1. For the mode 2-2, the terminal side needs to feed back a PMI of M Prefer sub-bands and a PMI of one wideband, and further needs to feed back a CQI of M Prefer sub-bands (calculated based on a PMI of M Prefer sub-bands) and a wideband CQI (calculated based on a PMI of one wideband).
Periodic feedback modes are semi-statically configured by a higher layer, and as shown in Table 2, can be divided into the following types:
TABLE 2Periodic feedback modePMI feedback modeNo PMISingle PMIPUCCHWidebandMode 1-0Mode 1-1CQI(Wideband CQI)feedbackUE SelectedMode 2-0Mode 2-1mode(Sub-band CQI)
For a terminal which is in a transmission mode 9 and is configured with eight CSI-RS antenna ports, a mode 1-1 can be divided into a sub-mode 1 and a sub-mode 2, and different sub-modes are configured via higher layer signaling PUCCH_format1-1_CSI_reporting_mode.
For periodic feedback, different feedback periods and sub-frame offset feedback types can be distinguished by classification as follows:
Type 1: reporting UE selected sub-band CQI;
Type 1a: reporting sub-band CQI and second PMI;
Type 2, Type 2b and Type 2c: reporting wideband CQI and PMI;
Type 2a: reporting wideband PMI feedback;
Type 3: reporting RI;
Type 4: reporting wideband CQI;
Type 5: reporting RI and wideband PMI;
Type 6: reporting RI and precoding matrix indicator (PTI).
Wideband feedback modes include a mode 1-0 and a mode 1-1, wherein the mode 1-1 can be further divided into a sub-mode 1 and a sub-mode 2. For the mode 1-0, the terminal side feeds back an RI of Type 3 and a wideband CQI of Type 4 for the transmission mode 3. For the mode 1-1, in addition to that eight CSI-RS ports are configured in the transmission mode 9, an RI of Type 3 and wideband CQIs and wideband PMIs of Type 2 are fed back in other transmission modes. For the sub-mode 1 of the mode 1-1 in which eight CSI-RS ports are configured in the transmission mode 9, the terminal side feeds back a joint code of an RI of Type 5 and a first wideband PMI and a joint code of a wideband CQI of Type 2b and a second wideband PMI. For the sub-mode 2 of the mode 1-1 in which eight CSI-RS ports are configured in the transmission mode 9, the terminal side feeds back an RI of Type 3 and a joint code of a wideband CQI of Type 2c, a first wideband PMI and a second wideband PMI. For UE selected sub-band CQIs, a mode 2-0 and a mode 2-1 are included. For the mode 2-0, the terminal side reports an RI of Type 3, a wideband CQI of Type 4 and a sub-band CQI of Type 1 in partial bandwidth for the transmission mode 3. For the transmission mode 2-1, in addition to that eight CSI-RS ports are configured in the transmission mode 9, an RI of Type 3, a joint code of wideband CQI and MPI of Type 2 and a sub-band CQI of Type 1 in partial bandwidth are fed back in other transmission modes. For the mode 2-1 in which eight CSI-RS ports are configured in the transmission mode 9, a joint code of a PTI and an RI of Type 6 is fed back. Then a feedback mode is further selected according to the value of the PTI; when PTI=0, a first PMI of wideband of Type 2a is fed back and then a joint code of a CQI of Type 2b wideband and a second wideband PMI is fed back; and when PTI=1, a joint code of a wideband CQI of Type 2b and a second wideband PMI is feedback, and then a joint code of a sub-band CQI of 1a and a second sub-band PMI is fed back.
In consideration that UE needs to feed back channel state information of a plurality of CSI-RS resources in the CoMP technology of R11, the UE shall feed back a plurality of pieces of CSI according to certain feedback rules, wherein in consideration of feedback rules, on one hand, it needs to be considered to reduce uplink feedback overhead as much as possible, and on the other hand, it needs to be considered to perform feedback by using a uniform mode as simple as possible to reduce possible collision probability during information feedback. However, at present, since feedback rules for CSI are still under discussion, there is no related technology for reference.